U.S. patent application number 12/270251 was filed with the patent office on 2010-05-13 for piezoelectric transducers with noise-cancelling electrodes.
This patent application is currently assigned to Avago Technologies Wireless IP (Singapore) Pte. Ltd.. Invention is credited to Osvaldo Buccafusca, Steven Martin.
Application Number | 20100117485 12/270251 |
Document ID | / |
Family ID | 42164544 |
Filed Date | 2010-05-13 |
United States Patent
Application |
20100117485 |
Kind Code |
A1 |
Martin; Steven ; et
al. |
May 13, 2010 |
PIEZOELECTRIC TRANSDUCERS WITH NOISE-CANCELLING ELECTRODES
Abstract
In a representative embodiment, an apparatus comprises a
transducer providing a first output; a capacitor providing a second
output; a first load impedance connected to the first output; a
second load impedance connected to the second output; and a
differential amplifier having a first input connected to the first
output and a second input connected to the second output.
Illustratively, the first load impedance is connected electrically
in parallel with the first input and the second load impedance is
connected electrically in parallel with the second input.
Inventors: |
Martin; Steven; (Fort
Collins, CO) ; Buccafusca; Osvaldo; (Fort Collins,
CO) |
Correspondence
Address: |
Kathy Manke;Avago Technologies Limited
4380 Ziegler Road
Fort Collins
CO
80525
US
|
Assignee: |
Avago Technologies Wireless IP
(Singapore) Pte. Ltd.
Singapore
SG
|
Family ID: |
42164544 |
Appl. No.: |
12/270251 |
Filed: |
November 13, 2008 |
Current U.S.
Class: |
310/319 |
Current CPC
Class: |
H04R 3/00 20130101; H04R
17/02 20130101 |
Class at
Publication: |
310/319 |
International
Class: |
H02N 2/18 20060101
H02N002/18 |
Claims
1. An apparatus, comprising: a transducer providing a first output;
a capacitor providing a second output; a first load impedance
connected to the first output; a second load impedance connected to
the second output; and a differential amplifier having a first
input connected to the first output and a second input connected to
the second output, wherein the first load impedance is connected
electrically in parallel with the first input and the second load
impedance is connected electrically in parallel with the second
input.
2. An apparatus as claimed in claim 1, wherein the transducer
comprises a piezoelectric transducer.
3. An apparatus as claimed in claim 1, wherein the capacitor
comprises a dielectric comprising a piezoelectric material.
4. An apparatus as claimed in claim 1, wherein the transducer and
the capacitor device are disposed over a common substrate.
5. An apparatus as claimed in claim 4, wherein: the transducer
comprises a piezoelectric transducer comprising upper and lower
electrodes; and the capacitor device comprises upper and lower
electrodes.
6. An apparatus as claimed in claim 5, wherein the upper electrode
of the transducer and the upper electrode of the capacitor device
are substantially concentric over a portion of an arc length.
7. An apparatus as claimed in claim 6, wherein the lower electrode
of the transducer and the lower electrode of the capacitor are
substantially concentric over a portion of the arc length.
8. An apparatus as claimed in claim 1, wherein a first noise signal
traversing from the first output is substantially identical to a
second noise signal traversing from the second output and at an
output of the amplifier, the noise signals are cancelled.
9. An apparatus as claimed in claim 8, wherein the first noise
signal and the second noise signal are of substantially the same
amplitude and phase.
10. An apparatus as claimed in claim 1, wherein the transducer is
configured to provide a signal from the first output to the first
input and the differential amplifier is configured to amplify the
signal.
11. An apparatus configured to transmit acoustic signals or receive
acoustic signals, or both, comprising: a first transducer providing
a first output; a second transducer providing a second output; a
first load impedance connected to the first output; a second load
impedance connected to the second output; and a differential
amplifier having a first input connected to the first output and a
second input connected to the second output, wherein the first load
impedance is connected electrically in parallel with the first
input and the second load impedance is connected electrically in
parallel with the second input.
12. An apparatus as claimed in claim 11, wherein the transducers
comprise piezoelectric transducers.
13. An apparatus as claimed in claim 11, wherein a first noise
signal traversing from the first output is substantially identical
to a second noise signal traversing from the second output and at
an output of the amplifier, the noise signals cancel.
14. An apparatus as claimed in claim 11, wherein the first and
second transducers are configured to provide signals that are
approximately .pi. radians out of phase second at the first and
second outputs.
15. An apparatus as claimed in claim 11, wherein the transducers
are disposed over a common substrate.
16. An apparatus as claimed in claim 11, wherein the upper
electrode of the transducers are substantially concentric over a
portion of an arc length.
17. An apparatus as claimed in claim 15, wherein the lower
electrode of the transducers are substantially concentric over a
portion of the arc length.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is related to commonly owned U.S.
patent applications: MULTI-LAYER TRANSDUCERS WITH ANNULAR CONTACTS
Ser. No. 11/11/604,478, to R. Shane Fazzio, et al. entitled
TRANSDUCERS WITH ANNULAR CONTACTS and filed on Nov. 27, 2006; and
Ser. No. 11/737,725 to R. Shane Fazzio, et al. entitled MULTI-LAYER
TRANSDUCERS WITH ANNULAR CONTACTS and filed on Apr. 19, 2007. The
entire disclosures of these related applications are specifically
incorporated herein by reference.
BACKGROUND
[0002] Transducers are used in a wide variety of electronic
applications. One type of transducer is known as a piezoelectric
transducer. A piezoelectric transducer comprises a piezoelectric
material disposed between electrodes. The application of a
time-varying electrical signal will cause a mechanical vibration
across the transducer; and the application of a time-varying
mechanical signal will cause a time-varying electrical signal to be
generated by the piezoelectric material of the transducer. One type
of piezoelectric transducer may be based on film bulk acoustic
resonators (FBARs) and bulk acoustic resonators (BAWs). As is
known, disposed FBARs and certain BAW devices over a cavity in a
substrate, or otherwise suspending at least a portion of the device
will cause the device to flex in a time varying manner. Such
resonators are often referred to as membranes.
[0003] As should be appreciated, among other applications,
piezoelectric transducers may be used to transmit or receive
mechanical and electrical signals. These signals may be the
transduction of acoustic signals, for example, and the transducers
may be functioning as microphones (mics) and speakers. As the need
to reduce the size of many components continues, the demand for
reduced-size transducers continues to increase as well. This has
lead to comparatively small transducers, which may be micromachined
according to technologies such as micro-electromechanical systems
(MEMS) technology, such as described in the related
applications.
[0004] While small feature size transducers do show promise, there
are certain drawbacks to known devices that deleteriously impact
their performance and thus their attractiveness for commercial
implementation. One such drawback is their propensity to provide an
unacceptably low signal-to-noise ration (SNR). FIG. 1 shows an
equivalent circuit of a transducer 101 (shown as an equivalent
voltage source (V.sub.piezo) and an equivalent capacitance
C.sub.piezo) connected to an amplifier 102. As is known, small
feature-size transducers comprise a comparatively small intrinsic
capacitance (C.sub.piezo) and provide a comparatively small
piezoelectric effect. These factors tend to limit the signal
amplitude due to the voltage divider circuit formed by Cpiezo and
RL. Moreover, the comparatively large electrode area, makes the
sensor susceptible to ambient noise (e.g., background
electromagnetic signals). Finally, the transducer 101 has a
comparatively large source impedance that when coupled with the
required large load resistance (R.sub.L) 103, can result in the
ambient noise's dominating the signal. Notably, as shown in FIG. 1,
at 104 the ambient electromagnetic noise from the transducer 101
`sees` a comparatively high impedance load resistance 103 which can
result in significant voltage noise at the amplifier's input
terminal. Thus, the comparatively low signal amplitude of the
desired signal from the transducer 101 is dominated by the ambient
noise, a problem further exacerbated by electronic noise in the
amplification circuit.
[0005] What is needed, therefore, is an apparatus that overcomes at
least the drawbacks of known transducers discussed above.
SUMMARY
[0006] In accordance with a representative embodiment, an
apparatus, comprises a transducer providing a first output; a
capacitor providing a second output; a first load impedance
connected to the first output; a second load impedance connected to
the second output; and a differential amplifier having a first
input connected to the first output and a second input connected to
the second output. Illustratively, the first load impedance is
connected electrically in parallel with the first input and the
second load impedance is connected electrically in parallel with
the second input.
[0007] In accordance with another representative embodiment, an
apparatus configured to transmit acoustic signals or receive
acoustic signals, or both, comprising: a membrane comprising a film
bulk acoustic (FBA) transducer providing a first output; a
capacitor device providing a second output; a first load impedance
connected to the first output; a second load impedance connected to
the second output; and a differential amplifier having a first
input connected to the first output and a second input connected to
the second output. Illustratively, the first load impedance is
connected electrically in parallel with the first input and the
second load impedance is connected electrically in parallel with
the second input.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The present teachings are best understood from the following
detailed description when read with the accompanying drawing
figures. The features are not necessarily drawn to scale. Wherever
practical, like reference numerals refer to like features.
[0009] FIG. 1 shows a simplified schematic diagram of an equivalent
circuit of a known transducer circuit.
[0010] FIG. 2A shows a simplified schematic diagram of an
equivalent circuit of a transducer circuit in accordance with a
representative embodiment.
[0011] FIG. 2B shows a simplified schematic diagram of an
equivalent circuit of a transducer circuit in accordance with a
representative embodiment.
[0012] FIG. 3A shows a top view of a transducer and a capacitor on
a common substrate in accordance with a representative
embodiment.
[0013] FIG. 3B shows a cross-sectional view of the transducer and
capacitor shown in FIG. 3A.
[0014] FIG. 3C shows a top view of a transducer and a capacitor on
a common substrate in accordance with a representative
embodiment.
[0015] FIG. 3D shows a cross-sectional view of the transducer and
capacitor shown in FIG. 3C.
[0016] FIG. 3E shows a top view of a transducer and a capacitor on
a common substrate in accordance with a representative
embodiment.
[0017] FIG. 3F shows a cross-sectional view of the transducer and
capacitor shown in FIG. 3A.
[0018] FIG. 4A shows a top view of a transducer and a capacitor on
a common substrate in accordance with a representative
embodiment.
[0019] FIG. 4B shows a cross-sectional view of the transducer and
capacitor shown in FIG. 4A.
DEFINED TERMINOLOGY
[0020] As used herein, the terms `a` or `an`, as used herein are
defined as one or more than one.
[0021] In addition to their ordinary meanings, the terms
`substantial` or `substantially` mean to with acceptable limits or
degree to one having ordinary skill in the art. For example,
`substantially cancelled` means that one skilled in the art would
consider the cancellation to be acceptable.
[0022] In addition to their ordinary meanings, the terms
`approximately` mean to within an acceptable limit or amount to one
having ordinary skill in the art. For example, `approximately the
same` means that one of ordinary skill in the art would consider
the items being compared to be the same.
DETAILED DESCRIPTION
[0023] In the following detailed description, for purposes of
explanation and not limitation, representative embodiments
disclosing specific details are set forth in order to provide a
thorough understanding of the present teachings. Descriptions of
known devices, materials and manufacturing methods may be omitted
so as to avoid obscuring the description of the representative
embodiments. Nonetheless, such devices, materials and methods that
are within the purview of one of ordinary skill in the art may be
used in accordance with the representative embodiments.
[0024] FIG. 2A shows a simplified schematic diagram of an
equivalent circuit 200 of a transducer circuit in accordance with a
representative embodiment. The circuit comprises a transducer 201,
which is illustratively a piezoelectric transducer based on film
bulk acoustic (FBA) transducer technology or bulk acoustic wave
(BAW) technology. Additional details of the transducer 201 are
described in the referenced applications to Fazzio, et al. and
below. Notably, the transducer 201 is a membrane device operative
to oscillate by flexing over a substantial portion of the active
area thereof. Moreover, the use of micromachined ultrasonic
transducers (MUTs) and piezoelectric MUTs are also contemplated for
use in the transducer of representative embodiments. These types of
transducers are known to those of ordinary skill in the art.
[0025] The circuit 200 also comprises a capacitor device 202, which
in the present embodiment is not subject to the piezoelectric
effect. As described below, the capacitor device is configured to
provide an electromagnetic noise signal for cancellation of a noise
signal garnered by the transducer 201.
[0026] The circuit 200 includes a load resistance 203 connected to
a first electrode 2a of the capacitor device 202 and a load
resistance 204 connected to a first electrode 1a of the transducer
201. As shown, in this configuration, the capacitor comprises a
second electrode 2b connected to ground and the transducer 201
comprises a second electrode also connected to ground. First
contacts 1a and 2a of the transducer 201 and the capacitor 202
provide a first output and a second output, respectively, which are
also connected to a first (illustratively positive) input and a
second (illustratively negative) input of a differential amplifier
205 of circuit 200. Notably, second contacts 1b, 2b of the
transducer 201 and the capacitor 202, respectively are connected to
ground.
[0027] In operation, an incident signal on the transducer is
converted from a mechanical wave to an electrical wave and emerges
from the first output as a signal. This signal is provided to the
positive input 205 and to the load resistance 204. However, because
of the parallel electrical connection shown, the signal `sees` a
comparatively high impedance value at the resistance 204, and the
voltage at the positive input of the differential amplifier 205 is
reduced by the voltage divider circuit comprised of the
transducer's output impedance and the resistance 204.
Unfortunately, noise can also be incident on the transducer 201 and
the electrical wiring connecting the transducer to the resistance
204 and amplifier 205. As described in connection with FIG. 1, the
magnitude of the (desired) signal from the transducer can be small
compared to the noise signal, and after amplification, can be lost
in the noise. In accordance with a representative embodiment,
beneficially the noise is substantially cancelled. In particular,
the first contact 1b of the capacitor 202 provides an output that
is connected to the second (in this example negative) input of the
differential amplifier 205. The noise signal is incident on the
capacitor 202 and the electrical connections interconnecting the
capacitor to the resistance 203 and amplifier 205 in a like manner
as on the transducer and other electrical node, and thus is
transmitted to the amplifier 205. However, because the noise signal
is provided to the negative input of the differential amplifier,
its magnitude is substantially the same after amplification but its
phase is opposite (i.e., everywhere .pi.-radians out of phase) to
the noise signal from the transducer 201. Thus, the noise signal
cancels and an output 206 from the amplifier is substantially the
amplified (desired) transducer signal.
[0028] FIG. 2B shows a simplified schematic diagram of an
equivalent circuit of a transducer circuit in accordance with a
representative embodiment. The equivalent circuit of FIG. 2B shares
many common features with the circuit of FIG. 2A, which are not
repeated in order to avoid obscuring the details of the present
representative embodiments.
[0029] As can be appreciated from a review of the embodiment of
FIG. 2B, instead of a capacitor 202, the second differential input
(in this case the negative input) of the presently described
embodiment is connected to a second transducer 207. The second
transducer 207 is substantially identical to the first transducer
201, however, is connected in an opposite manner to the second
input of the differential amplifier 205. The reversal of the
connections to effect the desired phase may be effect as described
in the referenced applications to Fazzio, et al. Thus, the phase of
the (desired) signal at the output of the transducer (i.e., at
contact 2b) is of substantially the same magnitude but opposite
phase as the (desired) signal at the output (i.e., at contact 1 a)
of the first transducer 201. By contrast, because the noise signal
is garnered by capacitive coupling at the transducers 201, 202, the
amplitude and phase of the noise signals provided at the respective
outputs 1a and 2b are substantially the same. Thus, outputs 1a and
2b provide (desired) signals of substantially opposite phase and
substantially in-phase noise signals to the first and second
(differential) inputs of amplifier 205. After amplification and
combination, the output 206 of the amplifier 205 comprises an
amplification of the sum of the (desired) signals from the
transducers 201, 207. In the illustrative embodiment, the amplitude
of the output 206 is approximately twice that of the desired
signals from the transducers 201, 207.
[0030] FIG. 3A shows a top view of transducer 201 and capacitor 202
on a common substrate 300 in accordance with a representative
embodiment. The transducer 201 and capacitor may be fabricated
using methods and materials in accordance with the teachings of the
referenced applications to Fazzio, et al., or using other known
methods and materials. Thus, fabrication sequences are omitted in
order to avoid obscuring the descriptions of the representative
embodiments.
[0031] The transducer comprises an upper electrode 301 and a
piezoelectric layer 302 disposed over the substrate 300. The
capacitor 202 comprises an upper electrode 303 disposed over the
substrate 300. As shown, the electrodes 301, 303 are substantially
circular and of approximately the same area. Contacts 1b and 2b are
connected to the upper electrodes 301, 303 and contacts 1a and 2a
are connected to lower electrodes (not shown in FIG. 3A). As should
be appreciated, the arrangement of FIG. 3A provides the transducer
201 and capacitor 202 with connections as shown in FIG. 2A.
[0032] FIG. 3B shows a cross-sectional view of the transducer 201
and capacitor 202 shown in FIG. 3A. The transducer 201 also
comprises a lower electrode 304, which spans a cavity 307 (commonly
referred to as a `swimming pool`), that provides a membrane
structure to the transducer 201. Thus, the transducer 201 may flex
over the cavity in response to electromagnetic or mechanical
signals incident thereon. The capacitor also comprises a lower
electrode 305, which is illustratively of the same shape as the
upper electrode 303. However, this is not essential, and an
electrode similar to that of lower electrode 304 can be provided.
The area of the capacitor is of course dictated by the area of
overlap of the upper and lower electrodes 303, 305. Finally, the
dielectric of the capacitor may be provided by piezoelectric layer
302 or by another suitable dielectric material. Usefully, the
capacitance of the capacitor 202 and the transducer 201 are
substantially the same so the noise signals delivered to the
amplifier 205 are substantially the same.
[0033] FIG. 3C shows a top view of transducer 201 and capacitor 202
on a common substrate 300 in accordance with a representative
embodiment. The transducer 201 and capacitor may be fabricated
using methods and materials in accordance with the teachings of the
referenced applications to Fazzio, et al., or using other known
methods and materials. Thus, fabrication sequences are omitted in
order to avoid obscuring the descriptions of the representative
embodiments.
[0034] The transducer comprises an upper electrode 308 and a
piezoelectric layer 310 disposed over the substrate 300. The
capacitor 202 comprises an upper electrode 309 disposed over the
substrate 300. As shown, the electrodes 308, 309 are substantially
circular and substantially concentric over a portion of an arc
length. Beneficially, the areas of the electrodes 308, 309 are
approximately the same. Contacts 1b and 2b are connected to the
upper electrodes 308, 310 and contacts 1a and 2a are connected to
lower electrodes (not shown in FIG. 3A). As should be appreciated,
the arrangement of FIG. 3C provides the transducer 201 and
capacitor 202 with connections as shown in FIG. 2A.
[0035] FIG. 3D shows a cross-sectional view of the transducer 201
and capacitor 202 shown in FIG. 3C. The transducer 201 also
comprises a lower electrode 311, which spans cavity 307 (commonly
referred to as a `swimming pool`), that provides a membrane
structure to the transducer 201. Thus, the transducer 201 may flex
over the cavity 307 in response to electromagnetic or mechanical
signals incident thereon. The capacitor 202 also comprises a lower
electrode 312, which is illustratively of the same shape as the
upper electrode 309. However, this is not essential, and an
electrode similar to that of lower electrode 311 can be provided.
The area of the capacitor 202 is of course dictated by the area of
overlap of the upper and lower electrodes 309, 312. Finally, the
dielectric of the capacitor may be provided by piezoelectric layer
310 or by another suitable dielectric material. Usefully, the
capacitance of the capacitor 202 and the transducer 201 are
substantially the same so the noise signals delivered to the
amplifier 205 are substantially the same.
[0036] FIG. 3E shows a top view of transducer 201 and transducer
207 on a common substrate 300 in accordance with a representative
embodiment. The transducers 201, 207 may be fabricated using
methods and materials in accordance with the teachings of the
referenced applications to Fazzio, et al., or using other known
methods and materials. Thus, fabrication sequences are omitted in
order to avoid obscuring the descriptions of the representative
embodiments.
[0037] Transducer 201 comprises an upper electrode 315 and
transducer 207 comprises an upper electrode 313. A piezoelectric
layer 314, which is disposed between the upper electrodes 313, 315
and lower electrodes (not shown in FIG. 3E), is provided. As shown,
the electrodes 313, 315 are substantially circular and
substantially concentric over at least a portion of an arc length.
Beneficially, the areas of the electrodes 313, 315 are
approximately the same. Contacts 1a and 2b are connected to the
upper electrodes 313, 315 and contacts 1b and 2a are connected to
lower electrodes (not shown in FIG. 3E). As should be appreciated,
the arrangement of FIG. 3E provides the transducers 201, 207 with
connections as shown in FIG. 2B.
[0038] FIG. 3F shows a cross-sectional view of the transducers 201,
207 shown in FIG. 3E. The transducer 201 also comprises a lower
electrode 316, which spans cavity 307 (commonly referred to as a
`swimming pool`), that provides a membrane structure to the
transducer 201. Thus, the transducer 201 may flex over the cavity
307 in response to electromagnetic or mechanical signals incident
thereon. The transducer 207 also comprises a lower electrode 317,
which is illustratively of the same shape as the upper electrode
315. Usefully, the capacitance of the transducer 201 and the
transducer 207 are substantially the same so the noise signals
delivered to the amplifier 205 are substantially the same.
[0039] FIG. 4A is a top view of a transducer structure 400
comprising `vertical` electrodes in accordance with a
representative embodiment. FIG. 4A shows the transducer structure
comprising a substrate 401, an upper electrode 405 and a second
piezoelectric layer 405. FIG. 4B shows a cross-sectional view of
the transducer structure 400 comprising `vertical` electrodes shown
in FIG. 4A. The transducer structure 400 may be fabricated using
methods and materials in accordance with the teachings of the
referenced applications to Fazzio, et al., or using other known
methods and materials. Thus, fabrication sequences are omitted in
order to avoid obscuring the descriptions of the representative
embodiments.
[0040] The structure 400 comprises the substrate 401, which
comprises a cavity 402 provided therein. A lower electrode 403 is
provided over the cavity 402 and substrate as shown. A first
piezoelectric layer 406 is provided over the lower electrode 403,
and an inner electrode 404 is provided over the first piezoelectric
layer 406. The second piezoelectric layer 407 is provided over the
inner electrode 404, and the upper electrode 405 is provided over
the second piezoelectric layer 407. The lower, inner and upper
electrodes 403, 405, 405 are provided in a substantially annular
arrangement relative to one another. In a representative
embodiment, the inner electrode 404 can be connected as the common
electrode (e.g., with a single contact for contacts 1b, 2a as
shown) between one set of electrodes and the other set of
electrodes. By appropriately connecting the outer electrodes to a
readout circuit, the two sets of electrodes can be used in a
differential configuration. For instance, if the neutral axis of
the membrane stack is placed in the center electrode, the upper and
common electrode would sense a piezoelectrically-developed voltage,
and the common and bottom electrode would sense a
piezoelectrically-developed voltage that is 180 degrees out of
phase to the first voltage.
[0041] In view of this disclosure it is noted that the transducers
and circuits useful for noise cancellation and amplification (gain)
can be implemented in a variety of materials, variant structures,
configurations and topologies. Moreover, applications other than
small feature size transducers may benefit from the present
teachings. Further, the various materials, structures and
parameters are included by way of example only and not in any
limiting sense. In view of this disclosure, those skilled in the
art can implement the present teachings in determining their own
applications and needed materials and equipment to implement these
applications, while remaining within the scope of the appended
claims.
* * * * *